Those bits of source show how strict vars works, but what I'm more interested (and couldn't figure out) is which part of the code determines whether or not a glob assignment will result in setting the IMPORT flag on the GV.

Its not commented/decorated, so my next move would be to fireup gitk or some such gitness to see how that block has changed (if at all) over the years ... and refresh my http://search.cpan.org/dist/illguts/index.html knowledge ... cause whatever I knew once I forgot :)